Future diesel engines will be equipped with exhaust gas after-treatment systems to allow them to comply with future emission legislation. Some of these systems have proven to be sensitive to the combustion products of the fuel and lubricant used in the engine. Certain types of systems are sensitive to phosphorus coming from the lubricant, others are sensitive to sulfur coming from both fuel and lubricant, yet others are sensitive to sulfated ash resulting from the combustion of fuel and lubricant. In order to ensure the durability of these different types of after-treatment systems, special lubricants are being developed that feature low levels of sulfated ash, sulfur and phosphorus. The most common of these lubricants provide low sulfated ash levels with reduced sulfur and phosphorus. Less common are low or no phosphorus lubricants that use specific, mostly sulfur or molybdenum based, zinc di-alkyl di-thiophosphate-replacement additives.
The guidelines for low emission diesel lubricants that will be commercialized in 2007 and 2008 are: (1) the sulfated ash must be equal to or lower than 1.0 weight percent for diesel engine lubricating oils and equal to or lower than 0.5 weight percent for passenger car diesel engine lubricating oils, (2) according to some engine builders, sulfur content of the lubricating oil must be less than 0.2 weight percent, while other engine builders allow up to a maximum of 0.4 weight percent, and (3) some engine builders require the maximum amount of phosphorus to be 0.08 weight percent, while other engine builders allow up to 0.12 weight percent of phosphorus.
The first generations of low emission diesel lubricating oils were formulated to meet the above guidelines using low levels of detergent and zinc di-alkyl di-thiophosphate. However, the expectation is that at some point in the future, the maximum sulfur and phosphorus content may be further reduced beyond where we expect the industry to go between now and 2010. Lubricating oils with no phosphorus were expected to provide no wear protection whatsoever. In an attempt to explore the boundaries of the performance envelope, we developed experimental lubricating oil formulations of the present invention containing essentially no phosphorus. Wear measurements were performed with these experimental lubricating oils in a heavy duty diesel engine and the results showed unexpectedly low cylinder liner wear levels.
A number of patents and patent applications have discussed methods for reducing emissions using low sulfur and low phosphorus lubricating oil compositions, but none have disclosed a low sulfur and low phosphorus lubricating oil composition comprising (a) borated dispersant and anon-borated dispersant (b) a molybdenum anti-oxidant and a phenolic anti-oxidant and (c) a low overbased sulfonate and a high overbased sulfonate, which despite containing essentially no zinc di-alkyl di-thiophosphate provides significant reduction in wear.
U.S. Pat. No. 4,623,473 discloses sulfur containing oil-soluble compositions which are useful as lubricating oil additives, particularly in lubricants containing little or no phosphorus. In one embodiment, the compositions of the invention comprise (A) at least one metal salt of at least one dithiocarbamic acid and (B) at least one oil-soluble sulfurized Diels-Alder adduct. Such lubricating oil compositions exhibit improved oxidation-corrosion inhibiting properties, anti-wear properties, and/or extreme pressure properties. These lubricating oil compositions contains less than 0.1 weight percent phosphorus also exhibit good compatibility with nitrile seals.
U.S. Pat. No. 4,859,353 discloses sulfur-containing borate esters for use in lubricants appropriate to modern oil requirements with reduced or zero amounts of phosphorus and without the need for large amounts and/or expensive forms of anti-oxidant and additional anti-wear additives.
U.S. Pat. No. 4,990,271 discloses a lubricating oil composition which comprises a major amount of an oil of lubricating viscosity and a minor amount of an additive formed by contacting molybdenum hexacarboxyl with di-xanthogens of the formula (ROCS2)2. Moreover, the lubricant compositions of this invention do not include phosphorus.
U.S. Pat. No. 6,159,911 discloses a diesel engine oil composition containing a lube oil base and one or more metallic detergents-dispersants selected from among a perbasic alkaline earth metal sulfonate, phenolate and salicylate. The total phosphorus content of the composition is suppressed to 100 parts per million by weight or less, to thereby provide diesel engine oil compositions having oxidation stability and wear resistance.
U.S. Pat. No. 6,162,770 discloses an un-sulfurized, alkali metal-free, detergent-dispersant composition having from about 40% to 60% alkylphenol, from 10% to 40% alkaline earth alkylphenol, and from 20% to 40% alkaline earth single aromatic-ring alkylsalicylate. This composition may have an alkaline earth double aromatic-ring salicylates as long as the mole ratio of single-ring alkylsalicylate to double aromatic ring alkylsalicylate is at least 8:1.
U.S. Pat. Nos. 6,331,510 and 6,610,637 disclose a lubricant containing (a) a synthetic base oil composition having an overall kinematic viscosity of at least about 4.8×10−6 m2/s (4.8 cSt) at 100° C. and a viscosity index of at least 110; (b) a dispersant-viscosity modifier; and (c) a sulfur-free functionalized hydrocarbyl-substituted phenol detergent provides improved valve train wear, with longer drain intervals, to heavy duty diesel engines.
U.S. Pat. No. 6,376,434 discloses a lube composition which is suitably used for diesel engines which exhaust large amounts of sulfur dioxides. The composition exhibits corrosion/wear preventive properties against sulfur dioxides. The lube composition includes a lube base oil, a component (A) which is a compound selected from a group consisting of overbased sulfonates of alkaline earth metal, overbased phenates of alkaline earth metals and overbased salicylates of alkaline earth metals, and a component (B) which is a bis-type succinimide compound.
U.S. Pat. Nos. 6,408,812 and 6,588,393 disclose a low sulfur consumable lubricating oil composition comprising a base oil, an acylated nitrogen-containing compound having a substituent of at least about 10 aliphatic carbon atoms; a sulfur content of about 5 to about 250 parts per million; said composition being characterized by the absence of an extreme-pressure additive comprised of metal and phosphorus.
U.S. Pat. No. 6,588,393 discloses a low-sulfur consumable lubricating oil composition comprising a base oil, an acylated nitrogen-containing compound having a substituents of at least 10 aliphatic carbon atoms, and a sulfur content of about 5 to about 250 ppm, such composition being characterized by the absence of an extreme pressure additive comprised of metal and phosphorus.
U.S. Pat. No. 6,723,685 discloses a lubricating oil composition comprising (a) an oil of lubricating viscosity having a viscosity index of at least 95; (b) at least one calcium detergent; (c) at least one oil-soluble molybdenum compound; (d) at least one organic ashless nitro-free friction modifier; and (e) at least one metal di-hydrocarbyl di-thiophosphate compound, the composition having a NOACK volatility of about 15 weight percent or less, from 0.05 to 0.6 weight percent calcium from the calcium detergent, molybdenum in an amount of at least 10 ppm from the molybdenum compound, and phosphorus from the metal di-hydrocarbyl di-thiophosphate compound in an amount up to about 0.1 weight percent.
U.S. Pat. No. 6,730,638 discloses a lubricating oil for internal combustion engines especially useful with fuels having less than 350 parts per million sulfur comprises a lubricating oil basestock, a boron-containing ashless dispersant, a molybdenum-containing friction reduction agent, a metal type detergent and zinc di-thiophosphate.
U.S. Pat. No. 6,777,378 discloses a lubricating oil composition comprising: (A) a base oil; (B) a molybdenum and sulfur-containing composition derived from a basic nitrogen-containing compound, a molybdenum compound and carbon disulfide; (C) a boron-containing compound; and (D) optionally a phosphorus-containing compound, provided the phosphorus content of the lubricating oil composition does not exceed about 0.1 weight percent.
U.S. Pat. No. 6,784,143 discloses the use of a minor amount of a detergent composition comprising one or more metal detergents which comprises metal salts of organic acids, wherein the detergent composition comprises more than 50 mole percent, based on the moles of the metal salts of organic acids in the detergent composition, of: (I) a metal salt of an aromatic carboxylic acid, or (II) a metal salt of a phenol, or (III) both a metal salt of an aromatic carboxylic acid and a metal salt of a phenol, in a lubricating oil composition for improving oxidation resistance of the lubricating oil composition, wherein the amount of phosphorus and sulfur in the oil composition is less than 0.09 mass % and at the most 0.5 mass % respectively, based on the mass of the oil composition. It has also been found that a detergent composition comprising more than 50 mole % of a metal salt of an aromatic carboxylic acid improves the reduction in wear in an engine.
U.S. Pat. No. 6,852,679 discloses a lubricating oil composition having less than 0.2 weight percent sulfur, less than 50 ppm chlorine, less than 50 ppm phosphorus, a NOACK volatility of 15 weight percent or less comprising an organo-molybdenum compound, an overbased calcium or magnesium salicylates, a dispersant and a supplemental anti-oxidant.
European Patent Application No. 92917678.2 (Publication No. EP 0 556 404 A2) discloses a lubricating oil composition prepared by compounding a base oil with a metal di-thiocarbamate and an oil-soluble amino compound. The composition contains scarcely any or no phosphorus and is excellent in wear resistance, extreme pressure properties, frictional characteristics, oxidation stability and coking resistance, thus being suitably usable as a lubricating oil for internal combustion engines of automobiles.
European Patent Application No. 00302646.5 (Publication No. EP 1 041 134 A1) discloses a lubricating oil composition which contains from about 50 to 1,000, preferably 50 to 500 parts per million of molybdenum from a molybdenum compound which is oil-soluble and substantially free of reactive sulfur, about 1,000 to 20,000, preferably 1,000 to 10,000 parts per million of a di-arylamine and 2,000 to 40,000 parts per million of a phenate. This combination of ingredients provides improved oxidation control and improved deposit control to the lubricating oil. This composition is particularly suitable for use as a crankcase lubricant.
European Patent Application No. 04016160.6 (Publication No. EP 1 498 471 A1) discloses an improved lubricating oil composition suitable for diesel engines comprising a major amount of at least one oil of lubricating viscosity and a minor amount of an alkylamine-alkylphosphate additive. The alkylamine-alkylphosphate additive comprises from at least 1.25 equivalents of alkylamine to 1.0 equivalents of alkylphosphate.
U.S. patent application Ser. No.10/344,696 (Publication No. US 2003/0182847 A1) discloses an additive used for a fuel oil or a lubricating oil composition for a diesel engine having a diesel particulate filter, and a fuel oil comprising the additive. The lubricating oil composition having a sulfated ash content of 1.0 weight percent or smaller, a sulfur content of 0.3 weight percent or smaller and a molybdenum content of 100 ppm or greater.
U.S. patent application Ser. No.10/277,295 (Publication No. US 2004/0077506 A1) discloses a lubricating oil composition having a total base number of at least about 8, comprising a major amount of oil of lubricating viscosity; an amount of one or more di-hydrocarbyl di-thiophosphate metal salt introducing into the lubricating oil composition no more than 0.06 weight percent of phosphorus; at least 1.2 weight percent of hindered phenol antioxidant; and boron and/or boron-containing compound or compounds in an amount providing the lubricating oil composition wit at least 200 ppm by weight of boron, all weight percentages being based on the total weight of the lubricating oil composition.
U.S. patent application Ser. No.10/649,572 (Publication No. US 2004/0127371 A1) discloses a lubricating oil composition for use in an internal combustion engine operated with a fuel having a sulfur content of less than 50 ppm, that contains a minor amount of at least one metal-containing detergent, which lubricating oil composition, when formulated for use in a diesel engine has a total ash content of less than 1.0 weight percent and when formulated for use in a gasoline engine has a total ash content of less than 0.7 weight percent.
U.S. patent application Ser. No.10/893,599 (Publication No. US 2005/0043191 A1) discloses a substantially zinc and phosphorus free lubricating oil meeting engine performance requirements contains an additive system containing metal detergents, at least one borated ashless dispersant, at least an amine anti-oxidant and a tri-nuclear molybdenum compound. The lubricant contains a minimum of 120 ppm boron and a minimum of 80 ppm molybdenum.
U.S. patent application Ser. No. 10/666,356 (Publication No. US 2005/0026792 A1) discloses a lubricating oil composition with very low phosphorus content, and having long life as evidenced by a reduction in viscosity increase, oxidation and nitration, comprises a major amount of a base oil of lubricating viscosity and a minor amount of a mixer of neutral and overbased metallic detergents, at least a zinc di-alkyl di-thiocarbamate anti-wear additive and at least a di-hydrocarboxylthiocarbamoyl.
U.S. patent application Ser. No.10/951,356 (Publication No. US 2005/0137096 A1) discloses an engine lubricant that is substantially free of zinc and phosphorus contains an anti-wear additive comprising borated 1,2-epoxy mixed polybutenes having an average carbon number in the range of C20 to C120.